The present invention relates to the art of heating air for use in a space to be heated and more particularly provides a unit to be installed in a flue, for example in an existing or newly constructed fireplace arrangement.
Numerous prior art devices are known which relate to the general subject matter of the present invention but none teaches or anticipates the present invention.
Briefly, Silfer, et al. U.S. Pat. No. 2,524,843 teaches an arrangement where air is received in conduits and is passed downwardly adjacent a smoke conduit carrying combustion products from a firebox but does not teach an arrangement to allow double pass heating of the air to be heated where at least one pass includes heating by virtue of convective flow of combustion products pass a conduit.
Black, U.S. Pat. No. 2,277,381 teaches an arrangement utilizing multiple outlets where air is as in Silfer, passed upwardly in conductive and convective heat relation with a smoke pipe but does not provide arrangement for heating of air as specified herein.
Additionally, Jones, U.S. Pat. No. 916,519 teaches an arrangement where air is heated while it is passed upwardly through a plenum chamber to adjacent floors.
Mueller, U.S. Pat. No. 2,376,173 teaches an arrangement where the air to be heated is passed downwardly through a conduit in a flue chamber but does not teach the heating arrangement taught by the subject invention.
Frye, U.S. Pat. No. 80,719 and Elmore, U.S. Pat. No. 2,231,258 teach arrangements similar to Mueller.
Additionally, Koopmeiners, U.S. Pat. No. 4,102,319 teaches an arrangement where a plenum chamber is provided above the firebox to heat air passed therethrough and Cage, U.S. Pat. No. 790 and Sherman, U.S. Pat. No. 4,043,313 teaches an arrangement to preheat outside air for use in a combustion chamber.
Finally, Hempel, U.S. Pat. No. 4,010,728, teaches an arrangement to conduit heat around a free standing fireplace system but could not be constructed as a unit to be inserted into existing flue systems as taught by the present invention.